1. Field of the Invention
The present invention generally relates to carrier assignment in a wireless communication system. Specifically, the present invention relates to a novel method of assigning carriers dynamically in consideration of priority factors and load conditions for each carrier in a sector for a CDMA2000 wireless communication system.
2. Description of the Related Art
A wireless communication system is generally known to consist of Access Terminals (AT) and a Radio Access Networks (RAN) connecting to a Core Network (CN). The wireless communication system may be operated according to various standards and/or different services. Depending on the standards, or the services provided, the RAN may include a plurality of Base Station Transceivers (BTS) and a Base Station Controller (BSC) or an Access Network Controller (ANC). A BSC or ANC may control a plurality of BTSs. While a BSC is connected to a Mobile Switching Center (MSC) for voice applications, the ANC is connected to a Packet Control Function (PCF) which in turn is connected to the Packet Data Serving Node (PDSN) for packet data communications. A MSC may be interconnected to other MSCs or to the Public Switched Telephone Networks (PSTN). The PDSN may be interconnected to the Internet or a Media Gateway; then to other networks.
The wireless communication system may be operated according to various protocols including, but not limited to, the Code Division Multiple Access (CDMA) protocol, the cdma2000 1× (1×), the cdma 1× Evolution Data Optimized (1×EV-DO), and the Universal Mobile Telecommunications Systems (UMTS). The protocols for the 1×, the 1×EV-DO, and the UMTS are collectively known as the third generation (3G) wireless technologies.
In a CDMA wireless communication system, all the BTSs deployed across a geographical service area can have a same carrier; which is the 1.25 MHz frequency band, with the Walsh codes and other codes distinguishing each user within the CDMA wireless communication system. More carriers can be allocated in the CDMA wireless communication system to increase the capacity by creating overlaying frequency coverage with some terminals serviced on one of the carrier frequencies while others are serviced on other carrier frequencies. This scenario is called a Multi-carrier System, which greatly increases the overall capacity of the system.
User mobility among all the BTSs of the CDMA wireless communication system is achieved through a mechanism called Handoff. The Handoff includes a Soft Handoff, a Softer Handoff, and a Hard Handoff (HHO) in a CDMA wireless communication system as well as a Virtual Handoff in an 1×EV-DO wireless communication system. For a Soft Handoff, the terminal can have multiple sectors as the serving sectors (Active Set) at the same time. In addition, the Active Set may change when the terminal moves from one sector to another sector. A Softer Handoff is a type of Soft Handoff for the sectors within the same cell (BTS). When the terminal moves from one carrier to another carrier, either within the same sector or cross different sectors, a HHO carries out. Unlike a Soft Handoff in which the link with the source does not break when the link with the target is established, a HHO stops the channel with the source then sets up the channel with the target. Therefore a HHO failure may introduce performance degradation such as drop calls, etc.
Therefore, the multi-carrier system is designed and operated in such a way to minimize the number of HHOs in a given voice communication and/or data transmission within the system. The present invention discloses a novel method for allocating the traffic among all the carriers to improve the efficiency of voice communication and/or data transmission in a multi-carrier wireless communication system.